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Department of Biological Sciences, Center for Tropical Disease Research and Training, University of Notre Dame, Notre Dame, IN 46556
Previous studies have shown that the ability of Mycobacterium tuberculosis to block a Ca2+ flux is an important step in its capacity to halt phagosome maturation. This affect on Ca2+ release results from M. tuberculosis inhibition of sphingosine kinase (SPK) activity. However, these studies did not address the potential role of SPK and Ca2+ in other aspects of macrophage activation including production of proinflammatory mediators. We previously showed that nonpathogenic Mycobacterium smegmatis and to a lesser extent pathogenic Mycobacterium avium, activate Ca2+-dependent calmodulin/calmodulin kinase and MAPK pathways in murine macrophages leading to TNF-
production. However, whether SPK functions in promoting MAPK activation upon mycobacterial infection was not defined in these studies. In the present work we found that SPK is required for ERK1/2 activation in murine macrophages infected with either M. avium or M. smegmatis. Phosphoinositide-specific phospholipase C (PI-PLC) and conventional protein kinase C (cPKC) were also important for ERK1/2 activation. Moreover, there was increased activation of cPKC and PI3K in macrophages infected with M. smegmatis compared with M. avium. This cPKC and PI3K activation was dependent on SPK and PI-PLC. Finally, in macrophages infected with M. smegmatis compared with M. avium, we observed enhanced secretion of TNF-, IL-6, RANTES, and G-CSF and found production of these inflammatory mediators to be dependent on SPK, PI-PLC, cPKC, and PI3K. These studies are the first to show that the macrophage proinflammatory response following a mycobacterial infection is regulated by SPK/PI-PLC/PKC activation of ERK1/2 and PI3K pathways.
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